The broad long-term objective of this project is to improve the pre-operative local staging of primary breast cancer by developing imaging techniques that accurately identify, localize and characterize clinically occult disease (malignancy). The specific aims of this proposal are as follows: 1). Assemble a database of 200 FDG-PEM studies acquired on patients with nonpalpable, mammographically-detected index lesions assessed as having at least a 50% risk of malignancy. 2). Determine performance metrics of FDG-PEM imaging. 3). Identify clinical allimitations of FDG-PEM imaging. We propose to determine the clinical impact of a novel positron emission mammography device which was developed to overcome the limitations of currently available whole body PET scanners and magnetic resonance imaging. This technology, which accurately depicts areas of increased glucose metabolism - characteristic of malignancy - demonstrates significantly improved spatial resolution and contrast resolution over conventional whole body PET scanners, allowing improved detection of subtle or otherwise occult foci of malignancy. FDG-PEM imaging will be performed on 200 patients immediately prior to core needle breast biopsy for mammographically detected abnormalities. These studies will be reviewed by radiologists with expertise in both breast imaging and PET, and the abnormalities will be assessed both qualitatively and quantitatively. Those lesions which demonstrate malignant histology will also be evaluated with magnetic resonance imaging. PEM, MRI, mammogrpahy and histology results will be correlated and statistically analyzed to determine their relationships. The sensitivity specificity, positive predictive value and negative predictive value for malignancy of PEM will be determined. We will also determine how well PEM characterizes the extent and distribution of carcinoma. We propose to determine the clinical impact of a novel positron emission mammography device, developed to overcome the limitations of currently available whole body PET scanners and magnetic resonance imaging, on patients recently diagnosed with breast carcinoma.